Omaha, Neb. — The U.S Army Corps of Engineers (Corps) Missouri River Water Management Office increased releases from Gavins Point Dam from 17,000 cubic feet per second (cfs) to 20,000 cfs in late December and early January to offset water lost to ice formation in anticipation of cold temperatures forecasted to enter the basin. 

“Extremely cold weather locked Missouri River flows into ice and caused dips in river stages below Gavins Point,” said Jody Farhat, chief of the Water Management Division.  “Releases will be adjusted, as necessary, to maintain downstream river stages.”  Releases will likely be reduced when more moderate temperatures return to the area.

Based on the current soil moisture and mountain and plains snowpack conditions, 2015 runoff in the Missouri River Basin above Sioux City, Iowa, is forecast to be 25.6 million acre feet (MAF).  Normal runoff is 25.2 MAF.  Annual runoff in 2014 was 35.0 MAF, which ranks eleventh highest in the 118 years on record.

The high runoff was the product of above normal mountain snowmelt runoff coupled with persistent summer rainfall in Montana and the Dakotas. “Rainfall events continued to occur in the upper basin through late August at a time of year when rainfall amounts historically diminish,” said Farhat.  “Fall releases were increased to ensure the full flood control storage zone is available for the 2015 runoff season, which typically begins around March 1.”

System storage ended December at 56.4 MAF, just 0.3 MAF above the base of the annual flood control zone.  Bitter cold temperatures in early January reduced inflows into the reservoir system as tributary rivers froze and system storage dropped sharply.  “Current system storage is 56.0 MAF, 0.1 MAF below the base of the annual flood control system,” said Farhat.  “The entire flood control capacity of the mainstem reservoir system stands ready to capture high runoff in the spring, reducing flood risk while providing good support to other authorized project purposes.”

Flow support for Missouri River navigation will likely be at full service levels for the first half of the 2015 season.  The actual service level will be based on the total volume of water stored in the reservoir system on March 15 in accordance with guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as the navigation season length, will be based on the actual July 1 system storage.

As of Jan. 1, the mountain snowpack was 101 percent of normal in the reach above Fort Peck Dam and 101 percent of normal in the reach from Fort Peck to Garrison Dam. Light plains snowpack has accumulated in western South Dakota and Montana with less snow seen in North Dakota.

“The Corps will continue to monitor the plains and mountain snowpack, and basin soil conditions through the winter and into spring to fine tune the regulation of the reservoir system based on the most up-to-date information,” said Farhat.